Certain types of analytical equipment, which may be referred to generally as sample platforms, are used for suspending or holding sample elements, with one possible objective of allowing these sample elements to be analyzed (or “read”) with as little signal contamination as possible from the surrounding substrate. Sample elements of particular interest exhibit luminescence, whereby materials such as minerals contained in these elements absorb energy upon irradiation that can be subsequently emitted, for example in the form of photons in the visible region of the electromagnetic spectrum. Thermoluminescence, in particular, is a form of luminescence in which electromagnetic radiation (normally visible light or near ultraviolet light) is emitted upon heating the sample element. Optically stimulated luminescence is another form of luminescence, in which electromagnetic radiation (also normally visible light or near ultraviolet light) is emitted upon exposing the sample element to light (e.g., having a wavelength that differs from that of the emitted electromagnetic radiation. The field of passive dosimetry is based on the use of these properties of some known materials to interact with ionizing radiation, the dose of which which can be later measured by using a reader to expose these materials to the appropriate energy form (e.g., heat or light at the appropriate temperature(s) or wavelength(s)) and measure the emitted light. Typical thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) are devices that include a substrate used to suspend or hold a sample element that exhibits thermoluminescence or optically stimulated luminescence, as the case may be. A dosimeter, such as a TLD or an OSLD, together with its respective reader and dose algorithm is referred to as a dosimetry system.
TLDs and OSLDs have developed significantly over the years, with the investigation into many types of materials exhibiting thermoluminescence and optically stimulated luminescence and their potential applicability to various areas of dosimetry. Such thermoluminescent and optically stimulated luminescent materials are capable of storing energy within their structure when irradiated, as electrons and holes become sequestered in “trapping centers” due to defects within the material. When the materials are exposed to heat (in the case of a thermoluminescent material) or to light (in the case of an optically stimulated luminescent material), electrons and holes recombine at “luminescence centers,” causing the emission of electromagnetic radiation, typically visible light. A reader measures this electromagnetic radiation, e.g., photons emitted in the visible region that constitute the signal, using a PMT (photomultiplier tube), solid-state detector such as charge-coupled devices (CCDs), or similar light transducers inside the device. If, according to preferred luminescent materials, one photon is emitted from each trap center, the measured signal is an index of the number of electron/hole pairs and is proportional to the previously absorbed radiation dose.
TLDs and OSLDs are commonly used for personal radiation monitoring, for example of those who may be exposed to radiation of greater than 3/10 of the dose equivalent limits. Monitoring in some settings, such as in the remediation of nuclear power plant accidents or in research laboratories investigating radiochemical applications, is considered essential to ensure compliance with maximum permissible dose standards. To this end, TLDs and OSLDs may employ multiple types of sample elements to more comprehensively determine doses received by an individual at specific depths within, and areas of, the body. For example, doses may be measured (1) at 10 mm to the whole body (Hp(10)), (2) at 3 mm to the lens of the eye (Hp(3)), and/or (3) at 0.07 mm to the extremities (Hp(0.07)). Applications for TLDs and OSLDs extend to environmental, neutron, and clinical monitoring, with commercially significant uses being in radiotherapy for cancer treatment, diagnostic radiation measurements, the dating of materials, and the analysis of meteorites.
Improvements in TLDs and OSLDs and, more generally, any types of substrates and associated sample platforms for suspending or holding sample elements that can be analyzed or read (by exposure to an appropriate energy source) in a reliable manner, are continually being sought.